1. Field of the Invention
The present invention relates to a receiving device for receiving time-multiplexed signals on one or more carrier frequencies, a transmitting system having multiple transmitting devices in order to cover a larger receiving region, and a method for operating a transmitting device.
2. Background Information
The European terrestrial digital audio system (DAB=digital audio broadcasting), which in the long term is intended to replace present-day FM/RDS radio, allows not only the transmission of audio programs, but also the transmission of additional digital data (PAD=program-associated data) at relatively high data rates.
In an OFDM signal used for this purpose, these additional data are coded in time-multiplexed fashion in the form of data symbols that are located at a defined time-related position within a frame. In an OFDM signal, such frames are transmitted successively in time and usually contain synchronization symbols, data symbols, and useful symbols. The structure of the frames is usually defined in the context of DAB.
Upon reception of a digital radio program, an OFDM signal is usually received and is demodulated and decoded in known fashion. The additional datum contained therein in accordance with the data symbol is available to a user. It is also desirable, however, for additional data from OFDM signals on other carrier frequencies to be made available to a user. This can be done by briefly switching the OFDM receiver to another carrier frequency, receiving the OFDM signal thereon, and demodulating and decoding the data symbol. This time period during which switchover to the other carrier frequency occurs should, however, be as short as possible, and the point in time should be selected so that at the time of the switchover, no useful symbol that is required for the radio program currently being listened to is being transmitted on the original carrier frequency. Because the point in time of the data symbol of the OFDM signal on the other carrier frequency is not known, however, in order to locate the data symbol it is necessary to switch over to the other carrier frequency for an unacceptably long time period to detect the data symbol. It may happen in this context that one or more useful symbols that are necessary for decoding the radio program are lost, and the user notices an interruption in the radio program.
It is therefore an object of the present invention to make available a receiving device, a method for operating a transmitting device, and a transmitting system, such that additional data can also be received from other time-multiplexed signals on other carrier frequencies without losing from the useful data stream any useful data that are necessary for decoding.